Mini Leslie...

[petemoore]

I was at a studio party-jam tonight, and a particitant told me of a mini-leslie, bout this big...[held his hands about a foot apart]...has a small rotating thing in it and a mic.
 Seems like a pretty straight foreward way to get an organic modulation...of course the component quility would be critical for excellent performance.
 I hadn't heard of one of these, thought of trying one before though.
 If you had a heavy, [very reflective inside] tube [tube like hose], you could get most types of delay modulation with speakers, mic, and valves, the organic way, Like a reverb chamber, but time/distance controlled...of course it would be of bohemoth proportion to get a long echo...right on the wacky track of possibilities...good thing there's other ways to do echo and modulation effects. I might take years to move that design to the venue !
 Anyway I thought the little sound spinner, speaker, mic thing sounded interesting, but also mechanically demanding to produce one. Without machines set up to help, anything I tried would probly look like uncle Fester and Mcgyver coordinated the build.
 Leslies arent that tuff to make with limited speed control, and woofer only.  I could do one in a day, starting with an old phonograph as the spinning device...maybe something else as a rotating plate driver next time. The effect is Real Sweet though.

[EdJ]

That sounds really interesting.i really like the sound of a leslie but the real ones don`t fit in my car.Guess i will have to dig into it too.
Ed

[petemoore]

Instead of a rotating baffle, a simple valve type affair would make a convincing tremolo IMO.
  Also I like the idea of running 'tube halls', for that sound  hose/tube [wrapping paper tube with voice resonating down it] sound. These would necessarily have to be heavy, and or isolated from outside vibration.
  Without having actually tried anything like this besides the homey leslie [which sounded really great with a celestion greenback powering it], I can say the concept is 'sound'.

[bwanasonic]

http://www.songworks.com/rotary.htm

Kerry M

[petemoore]

The clip probably doesn't sound like the effect in a room, with the waves bouncing all over the walls etc.
 Micing this isn't going to capture it's sound, or it won't be easy to get the full effect using mics. It'll sound more like a tremolo, just as the clip does, capturing the chorus effect in a recording... :?
 Looks very good with the celestion [I tried some different types in my homey-leslies, and the greenbacks were chosen from those tried], and the endorsements...low noise long life bearings and nice speed control...probly pretty cool !!!

[RickL]

One cost effective way of doing this in a fairly small package to to find an old home organ with a rotating speaker in it and repackage just the speaker and motor. I did this with the speaker from an organ I was given. The final box was about 2'x1.5'x1'. I had to power it with an external amp and it needed to be miked even in the small rooms I was playing at the time but it beat hauling around the Leslie 210 (small for a Leslie) that I was using at the time. I was running the organ from my Guitorgan through it.

[Craig V]

An easy and pretty cheap way to get a Leslie tone is go on Ebay and search for "Leslie Tremolo Unit" which will probably be pulled from an organ and be an 8 or 10 inch speaker with the foam rotor attached to a baffle and come with the motors, which you will probably have to wire, but its easy, just connect wall current to which motor you want to run, and you will need to build a cabinet for it or leave it as is which looks kind of cool, that is what I did, which has the 8 inch speaker, I kind of wish I had a 10 incher, but this does the job quite well, although its not as deep as a full Leslie cabinet, but it works well, its more of a "Us and them" by Pink Floyd leslie tone compared to the deep on the bridge of "Badge" by Cream (Eric Clapton).

That was one long sentence  

[Mark Hammer]

I'm fortunate enough to have one of these little styrofoam "cheese wheel" Leslies with an 8" speaker.  They can sound great.

I, too, pondered the possibilities of making a small Leslie with 4" or less speakers.  One of the ways you can do this is all-electronic.  If you had an array of 4 or 6 speakers, each with their own mini-amp (386, LM380, TDA2003, etc), and a VCA controlled by a Shepard function generator (see my site for an example), you could electronically mimic a moving sound source by having one speaker loudest and the others trailing it be staggered loudnesses.  As far as the air is concerned around the unit, it doesn't really matter whether the moving sound source got there via a motor, a VCA, or the USS Enterprise transporter.  It is the clash between the air pressure front produced by a sound wave generated from THIS point in space, as opposed to THAT point in space, which produces the Doppler effect.  Indeed, I believ Roland produced just such a unit in the early 80's which they called the "Revo"; an entirely non-mechanical rotating speaker unit.

In retrospect, although the all-electronic thing CAN work, I have my doubts about it working all that well with small speakers in a small physical space.  The chief reason is that time=space (or space=time).  

I'll explain.  To have a useful modulation rate, the sound source has to take a certain period of time to complete one rotation.  So, for a 1hz modulation rate, it needs to take about 250msec to go from North to West, another 250msec from West to South, and so on.  The cancellations produced in those relevent parts of the frequency spectrum that make for an audible doppler effect (i.e., one a human ear can actually hear) need the south, west, north and east wave fronts to be a certain distance apart.  If the circumference of that moving sound/wave front is too small, that critical distance is not achieved.  *IF* you could mimic that big a circumference electronically, you could probably get the sound desired, but mimicking a circle with a 16" or greater diameter would take a whole heap of 4" speakers to provide smooth contiguous movement of the sound source in a circle.  And at that point, you have so many speakers, amps, VCAs, etc., that it turns into an acadmic exercise (i.e., can it be done) rather than anything practical, or even acoustically desirable.

I don't think I explained that one particularly well, but the punch line is that it is unlikely for a micro-Leslie with anything less than a certain diameter (or something that isolates the sound field in a manner that mimics a much wider circumference, like a narrow horn) to sound Leslie-ish enough for most tastes.

[Quackzed]

I was thinking about this very idea... i started sketching out a mini leslie type box...only instead of a baffle it used a rotating mic and a speaker inside a damped soundproof box...then i realized i didn't need the box ...  or the speaker .... just a rotating mic(i was gonna do stereo)and a block to isolate them from each other... 
it's all been done...theres nuthin' new under the sun...
another one of my brainchildren turns out to be adopted.
I don't care...i'm still gunna make one.
... I've invented so many things that were already invented...you ever hear of the wheel?

[calpolyengineer]

Mark,
I don't think that having a circle of speakers with varied volumes would give you a doppler shift. It would sound like a circular panner. To get the frequency shift, the speaker does need to be moving. When the speaker is moving it causes the sound to have shorter wavelengths in the direction it is moving and longer wavelengths in the opposite direction. Since the speed of sound isn't changing, the frequency must go up for the shorter wavelengths and down for the longer wavelengths. Your idea would make a sound that is similar to a Leslie, but it wouldn't sound quite right because there wouldn't be any frequency shifts, volume (amplitude) shifts.

-Joe

[Mark Hammer]

Mark,
I don't think that having a circle of speakers with varied volumes would give you a doppler shift. It would sound like a circular panner. To get the frequency shift, the speaker does need to be moving. When the speaker is moving it causes the sound to have shorter wavelengths in the direction it is moving and longer wavelengths in the opposite direction. Since the speed of sound isn't changing, the frequency must go up for the shorter wavelengths and down for the longer wavelengths. Your idea would make a sound that is similar to a Leslie, but it wouldn't sound quite right because there wouldn't be any frequency shifts, volume (amplitude) shifts.

-Joe

Thanks for digging this nugget up.
One of the things I like about myself is that I hang onto pieces of paper for the longest time...and sometimes they come in handy.
Turns out Roland used this very principle in their Revo series of rotary-like speaker cabinets.  My Roland catalog from 1980 or 82 (pet rabbit chewed off a corner of the catalog before I retrieved it!) shows 6 models of the Revo.  The catalog blurb says "Electronic rotary sound; no mechanical parts to wear out.  Use with any organ or other keyboard instrument.  The Revo Sound System includes chorus for better stereo sound.  You sound great even in a room with bad acoustics!"

The RD-150 and 155 systems sport four 20cm speakers and one 38cm speaker.  The 125 model sports three 20cm speakers and a single 30cm.  The model 250 has six of the 20cm speakers.  They all had speed controls and "resonance changeover" controls.

I think I tried one of these or heard someone try one out in a music store at that time.  It sounded pretty good, although I did not have any opportunity to A/B it with a true Leslie.
My sense is that the effect would be closer to a true moving speaker, the more drivers there were to pan with.  I gather the 250 had the most authentic sound of the lot for that reason, and was not simply more powerful.  I don't think the ear really cares if the sound source is a physical object moving in space or if the physical object is stationary and the sound is simply electronically relocated across sources.  The format of that panning and source movement is likely to be important, and my guess is that it involves switching sources cyclically, as opposed to something like smooth panning.  At the same time, the fewer sources there are for that distribution, the more likely it is to sound like a cheezy panner in the absence of any other electronic wizardry. 

As I also noted, the units incorporated "chorus" though there is no clue about the implentation.  It may well be that leading and lagging signals are separated by delay in order to increase apparent movement.  Separate routing of dry and wet signals was something Roland was already doing by this time to great effect.  Turning a single page in that same catalog takes me from the Revo to the Jazz Chorus amps that used one channel/speaker for dry and another for wet.